Minimum Updates to Make Bitwise OR Equal to Target - Microsoft Top Interview Questions

Problem Statement :

You are given three positive integers a, b and target. 

Consider an operation where you take either a or b and update one of the bits to 1 or to 0.

Return the minimum number of operations required to make a | b = target.


1 ≤ a, b, target < 2 ** 31

Example 1


a = 2

b = 4

target = 8




  10 = a

 100 = b

1000 = target

We need to first unset a and bs 1 bits to make them zero. Then we can set a directly to 8.

Solution :


                        Solution in C++ :

int solve(int a, int b, int target) {
    int ans = 0;
    for (int i = 0; i < 32; ++i) {
        int mask = 1 << i;
        if (target & mask) {
            if ((a & mask) || (b & mask)) continue;
        } else {
            if (a & mask) ans++;
            if (b & mask) ans++;
    return ans;

                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(int a, int b, int target) {
        int aExtra = a & ~target;
        int bExtra = b & ~target;
        int targetExtra = target & ~(a | b);
        return Integer.bitCount(aExtra) + Integer.bitCount(bExtra) + Integer.bitCount(targetExtra);

                        Solution in Python : 
class Solution:
    def solve(self, a, b, target):
        res = 0
        while a != 0 or b != 0 or target != 0:
            if (a & 1) | (b & 1) != (target & 1):
                res += 1
                if (a & 1) == (b & 1) == 1:
                    res += 1
            a >>= 1
            b >>= 1
            target >>= 1
        return res

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